Grasses and endophytic fungi: Difference between revisions
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The relationship between certain grasses and endophytic | The relationship between certain grasses and [endophytic http://en.wikipedia.org/wiki/Endophyte] fungi is symbiotic [http://en.wikipedia.org/wiki/Symbiotic]. The most common benefit that the plant receives from the endophytic fungi is increased resistance to herbivores and other environmental stresses (2). The endophytic fungi produce toxic alkaloids [http://en.wikipedia.org/wiki/Alkaloid] that can deter herbivores or reduce the performance of the herbivore(article 2). The grass provides food and shelter for the fungi in return (fungus wiki 142). The discovery of this relationship occurred when cattle grazing on the infected grass developed delirium and “livestock staggering”(2). | ||
==Biological interaction== | ==Biological interaction== | ||
Revision as of 06:53, 6 April 2011
Introduction
The relationship between certain grasses and [endophytic http://en.wikipedia.org/wiki/Endophyte] fungi is symbiotic [1]. The most common benefit that the plant receives from the endophytic fungi is increased resistance to herbivores and other environmental stresses (2). The endophytic fungi produce toxic alkaloids [2] that can deter herbivores or reduce the performance of the herbivore(article 2). The grass provides food and shelter for the fungi in return (fungus wiki 142). The discovery of this relationship occurred when cattle grazing on the infected grass developed delirium and “livestock staggering”(2).
Biological interaction
The relationship between endophytic fungi and grasses is systematically symbiotic. The defensive and most successful fungal endophytes produce no visble effects in plants. Even so, there are a variety of advantages the grass receives from the fungi. This includes enhanced insect herbivory resistance, fungal disease resistance, enhanced vegetative growth, and increased drought tolerance.
The endophytic fungi also receive benefits including greater access to nutrients, protection from desiccation, protection from surface feeding insects, and protection from parasitic fungi and competition among other microbes(1). Depending on both the fungal and grass species, the relationship can be very specific or have a wide range of possible host grass plants.
Most symbiotic relationships are pleitropic (balanced) in the Epichloe and Neotyphodium genera. The other symbiotic relationships include nonpathogenic symbionts that transmit vertically by systematic infection of seed(asexual). This type of symbiosis is highly beneficial to the host. On the opposite end of the spectrum, there are antagonistic symbionts and transmit horizontally (contagious) and suppress host seed production(sexual).
Influence on other organisms
Mammals
Endophytic Fungi produce alkaloids (ergotoxin and indolediterpenoid tremorgens) that are toxic to mammalian herbivores. The species that most effects mammals are from the genus Neotyphodium. When mammals consume grass infected with the fungi, different neurological effects take place(1)
Cattle that graze on infected tall fescue grass can develop a condition known as "fescue foot". Over a long period of time, blood is reduced to extremities which eventually leads to the tail or hoove rotting off..
When animals graze on perennial rye grass infected by N.lolii, they may develop uncontrollable spasms. Another grass, sleepy grass, contains a Neoptyphodium that causes horses to sleep for two to three days (1).
Insects
Insects react and have different reactions to the toxin, but the overall pattern is that the endophytic fungi promote anti-herbivory benefits in native grasses. The alkaloid toxin that protects against herbivory are lolines and peramines (3).
Microbes
Fungal endophytes, in particluar Neotyphodium, are shown to reduce colonization of arbuscular mycorrhizal fungi on the host (4). Mechanism by which the endophyte reduces colonization is through allelopathic effects. The affect on the mycorrhizal fungi from endophytic fungi is an important process to understand. Mycorrhizae promote plant growth and overall, grassland ecosystems (4).
Niche
Endophytic fungi are distributed in the intercellular portion of the host and restricted to above ground growth (1). This growth occurs in the floret, sheath, stem, and leaf tissues of the developing grass seedling and maturing plant (2). Endophytic fungi are considered an intercellular foliage symbiont and associations are established at the seedling stage and are long-lived. All grass fungal endophytes are capable of growth on a wide range of simple carbon sources. The endophytic fungi need amino acids, simple sugars, and a variety of vitamins to survive and are acquired from the apoplasm of the host (1).
Microbial processes
One of the more important processes involved in the endophytic fungi - grass relationship is the production of alkaloids. There are four different kinds of alkaloids produced, and each have different consequences. The first two, lolines [3] and peramines have no other close chemical relatives. These two toxins protect against herbivory. The other two are ergotoxins [4] and indolediterpenoid tremorgens which are the toxins that affect the mammalian neurological system. These toxins help prevent insect and mammalian herbivory and increases plant growth and vigor. The endphytes must produce stromata in order to reproduce sexually. The stromata helps flow of nutrients from the host to the fungal component of stroma. Plant tissues within the stroma can be modified by the endophytes to increase flow of nutrients into the mycelium (1).
Key Microorganisms
The endophytic fungi are within the family Clavicipitaceae. The most common genera of endophytic fungi include Balansia, Epichloe, and Parepichloe. Balansia is said to be derived from epibiotic species of that genus. The endophytic component had evolved only in B. claviceps and is limited to the Americas. The Epichloe and Parechloe have two separate lines of evolution and are phylogenetically different.
Current Research
Enter summaries of recent research here--at least three required
References
1. Bacon, Charles W, White, James F., comp. Microbial Endophytes. New York: Marcel Dekker Inc., 2000.
2. http://www.uri.edu/ce/factsheets/sheets/endophyte.html
3. Crawford, Kerri M. et al. Fungal endophytes of native grasses decrease insect herivore preference and performance. 29 June 2010. Sringer-Verlag 2010.
4. Antunes, P.M. et al. Even after death the endophytic fungus of Schedonorus phoenix reduces the arbuscular mycorrhizas of other plants. Functional Ecology 2008, 22, 912-918.
Edited by <your name>, a student of Angela Kent at the University of Illinois at Urbana-Champaign.
